Time division multiplexed (TDM) wireless communication systems are know to comprise a central controller that allocates a plurality of wireless communication resources, via base stations operably connected to the central controller, among a plurality of communication units. In such systems, the communication units (i.e., hand-held or in-car mobile radios) are assigned wireless communication resources in the form of a radio frequency (RF) carrier divided by time, i.e., time slots. As known in the art, the communication units are typically arranged into one or more communication groups. Such communication groups, or talk groups, allow radio users with similar work functions or goals to immediately communicate with one another.
Upon receiving a group call request from a communication unit affiliated with a communication group, the central controller allocates wireless communication resources for use by the communication group. The communication unit can then transmit voice signals via the allocated resource and any target units intended to receive the voice signals (i.e., communication group members) can monitor the allocated resource.
As noted above, it is possible for a communication unit to be associated with more than one communication group. Furthermore, such communication groups are often arranged in an hierarchical fashion. For example, in a communication system used by a law enforcement agency, all officers, from patrolmen up to the chief of police, would be included in a first communication group. A second, smaller communication group would comprise supervisory officers up to the chief. Finally, a still-smaller third communication group would include only the chief of police and his district commanders. In essence, each succeeding communication group becomes more exclusive in that fewer members are allowed to participate in group calls intended for those groups. Concurrent membership in multiple communication groups allows certain members, e.g., the chief of police, to participate in various group calls as necessary.
In current systems, however, it is not possible for a communication unit to participate in more than one group call at any time. This inability to participate in more than one talk group can be unduly burdensome on users of the system. Again using the current example, if an emergency situation arises, the chief of police may need to participate in communications with officers at the scene of the incident, and at the same time discuss strategy with the supervisory officers only. Using current systems, the chief of police would be forced to participate in communication with one group or the other, but not both talk groups at the same time. Therefore, a need exists for a method which allows communication units to participate in more than one group call at the same time.